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AN INVESTIGATION OF BETA-CAROTENE ATMOSPHERIC OXIDATION PROCESS IN THE ANIONIC SURFACTANT SYSTEM IN ABSENCE AND PRESENCE OF VITAMIN C
DEPARTMENT OF RADIOCHEMISTRY AND COLLOID CHEMISTRY, FACULTY OF CHEMISTRY UMCS
b-Carotene is a very efficient antioxidant acting as the most important physiological quencher that protects cellular against singlet oxygen damage and also is vitamin A precursor for almost all species. Several studies have shown that b-carotene in organic solvents can easily lose two electrons by electrochemical or chemical oxidation. The resulting cation and dication are very stable in these media. In natural systems, in which the environment is very different from that in organic solvents, radical cations of carotenoids are usually short-lived. In organic solvents, carotenoids can move freely, whereas in natural systems they are fixed in their positions and have an ordered environment, which can change their behaviour. The matrix dependence is the reason for our study of b-carotene in micelles in which b-carotene can be arranged in an ordered way. In addition to this ordered environment, micelles also provide an interface of a hydrophilic and a hydrophobic region. This interface can be a simple model for studying the processes occurring at biological membranes.
In presented paper, we described the atmospheric oxidation of b-carotene in the anionic surfactant system as well as the role that the ascorbic acid presence plays towards b-carotene action. One should recall that what has been observed in vitro, may not be automatically transferred to the living system.
Our investigations are based on well-known micellar system pentanol/ water/ sodium dodecyl sulphate. It contains the inverse micellar solution, the basis for W/O microemulsions (at Figures presented below: 6% SDS, >72% water), a bicontinous part (at Figures: 6% SDS, 72% water, 22% pentanol), and the aqueous micellar solution that forms the basis for the O/W microemulsions (at Figures: 6% SDS, <72% water).
The kinetics of the b-carotene and the ascorbic acid decomposition in the system was determined by ultraviolet spectroscopy.
In Fig.1 the decrease of b-carotene concentration in microemulsions of different type is presented. As can be expected b-carotene is more stable in W/O microemulsion than in O/W one. In micelles, the long conjugated hydrocarbon chain of b-carotene is located in the hydrophobic region, but its terminal polar group may be in contact with water and subject to oxidation.
Fig.1. 0.0005% b-Carotene decomposition in the system: SDS, pentanol, water.
Vitamin C addition into the system does not change antioxidant properties of b-carotene; it is still better antioxidant in O/W microemulsion - Fig.2.
Fig.2. 0.0005% b-Carotene decomposition in the system: SDS, pentanol, water, 0.002% vitamin C (initially).
In Fig.3 one can see that the presence of b-carotene strongly influences vitamin C antioxidant action. Vitamin C antioxidant capability increases with the decrease of pentanol concentration in the system i.e. in O/W microemulsion. These results are in contrast to the results presented earlier for an atmospheric oxidation of vitamin C  and the influence of vitamin C on vitamin E oxidation kinetics  in SDS micellar solutions where vitamin C was suggested to be better antioxidant in W/O microemulsion system.
Fig.3. 0.002% Vitamin C decomposition in the system: SDS, pentanol, water, 0.0005% b-carotene (initially).
Significant antioxidant synergism and novel mutual protection of b-carotene and vitamin C was found in anionic surfactant systems.
 M. Szymula, J. Szczypa and S.E. Friberg, J. Disperson Sci. Technol. in press.
 M. Szymula, J. Disperson Sci. Technol., 21 (2000) 983.